Lithographic objective having a first lens group including only lenses having a positive refractive power

ABSTRACT

A projection objective includes a first lens group (G 1 ) of positive refractive power, a second lens group (G 2 ) of negative refractive power and at least one further lens group of positive refractive power in which a diaphragm is mounted. The first lens group (G 1 ) includes exclusively lenses of positive refractive power. The number of lenses of positive refractive power (L 101  to L 103;  L 201,  L 202 ) of the first lens group (G 1 ) is less than the number of lenses of positive refractive power (L 116  to L 119;  L 215  to L 217 ) which are mounted forward of the diaphragm of the further lens group (G 5 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 10/873,292, filed Jun. 23, 2004, now U.S. Pat. No. 7,023,627, which is, in turn, a continuation application of application Ser. No. 10/025,605, filed Dec. 26, 2001, now U.S. Pat. No. 6,788,387, claiming priority from German patent application 100 64 685.9, filed Dec. 22, 2000, and all incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a projection objective for microlithography which has at least two lens groups which have positive refractive power.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,990,926 discloses a projection lens system for use in microlithography and this lens system has three bellied regions, that is, three lens groups of positive refractive power. The objective is viewed in the direction of the propagation of the light. Here, the first lens group includes only positive lenses and the wafer end numerical aperture is 0.6.

U.S. Pat. No. 5,969,803 discloses a projection objective for use in microlithography and this lens system includes three positive lens groups. The numerical aperture again is 0.6 and the objective here is a purely spherical objective.

U.S. Pat. No. 4,948,238 discloses an optical projection system for microlithography wherein, at the wafer end, the last two lenses have respective aspherical lens surfaces for improving imaging quality. The aspherical lens surfaces are arranged facing toward each other.

The projection systems known from the above U.S. Pat. No. 4,948,238 have a low number of lenses. Especially, the numerical aperture, which can be made available by means of this objective, is only 0.45.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a projection objective for microlithography which has a high numerical aperture as well as excellent imaging qualities.

The projection objective of the invention includes: a first lens group of positive refractive power; a second lens group of negative refractive power; at least one additional lens group having positive refractive power and the one additional lens group having a diaphragm mounted therein; the first lens group including only lenses having positive refractive power; the one additional lens group having a number of lenses of positive refractive power arranged forward of the diaphragm; and, the number of lenses of positive refractive power of the first lens group being less than the number of lenses of positive refractive power of the one additional lens group arranged forward of the diaphragm.

A projection objective is provided which has an especially high numerical aperture while at the same time having a low structural length because of the following measures: a first lens group which is so configured that this lens group comprises only lenses of positive refractive power and the number of lenses of positive refractive power of the first lens group is less than the number of the positive lenses which are mounted forward of the diaphragm of the additional lens group of positive refractive power.

In the input region of the objective, an expansion of the input beam is avoided by providing the first lens group which has only lenses of positive refractive power. Because of this measure, this first lens group can be configured to be very slim, that is, the lenses have a small diameter. In this way, less material is needed in the first lens group, on the one hand, and, on the other hand, the structural space, which is needed to accommodate this lens group, is reduced. This structural space can be used to increase the numerical aperture by providing additional positive lenses forward of the diaphragm.

For an especially slimly configured first lens group, it is possible to shift the Petzval correction into these follow-on lens groups of positive refractive power because of the structural space obtained with a slight enlargement of these follow-on lens groups of positive refractive power. An especially large contribution to the Petzval correction is supplied by the positive lens group in which the diaphragm is mounted in combination with the strong beam narrowing forward of this group via a strong negative refractive power.

Preferably, the diameter of the lenses of the first lens group is less than 1.3 times the object field.

It has been shown to be advantageous to provide at least one lens having an aspheric surface in the first lens group. This aspheric surface contributes to improving the imaging quality of the objective.

It has been shown to be advantageous to provide aspheric lens surfaces in the first lens group which deviate by more than 300 μm compared to the best fitting spherical lens surface. The arrangement of such an asphere on the object end lens surface of the first lens of the lens arrangement has been shown to be advantageous. These intense asphericities close behind the reticle are especially effective in order to correct the field-dependent aberration. The extent of the asphericity is dependent upon the beam cross sections and on the input aperture which is always less than the output aperture. Even though the deviation to the sphere is great, a simple asphere form generates the most favorable contribution to the total aberration correction. As a consequence of the simple asphere form, this asphere form remains nonetheless easy to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings wherein:

FIG. 1 is a schematic showing the assembly of a projection exposure system;

FIG. 2 is a schematic side elevation view of a projection objective for 248 nm having a numerical aperture of 0.8;

FIG. 3 is a schematic side elevation view of a projection objective for 193 nm having a numerical aperture of 0.8; and,

FIG. 4 is a schematic side elevation view of another projection objective for 248 nm having a numerical aperture of 0.8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

First, the configuration of a projection exposure system will be described with reference to FIG. 1.

The projection exposure system 1 includes an illuminating unit 3 and a projection objective 5. The illuminating unit can, for example, be an excimer laser having a wavelength of less than 250 nm. The projection objective 5 includes a lens arrangement 19 having an aperture diaphragm AP. An optical axis 7 is defined by the lens arrangement 19. Different lens arrangements are explained hereinafter with reference to FIGS. 2 and 3. A mask 9 is mounted between the illuminating unit 3 and the projection objective 5 and the mask is held in the beam path with the aid of a mask holder. Masks 9 used in microlithography have a micrometer-nanometer structure. This structure is imaged on an image plane 13 by means of the projection objective 5 demagnified up to a factor of 10 (demagnified especially by a factor of 4). A substrate 15 or a wafer, which is positioned by a substrate holder 17, is held in the image plane 13.

The minimal structures, which can still be resolved, are dependent upon the wavelength λ of the light, which is used for the illumination, as well as on the image-end numerical aperture of the projection objective 5. The maximum achievable resolution of the projection exposure system 1 increases with a decreasing wavelength λ of the illuminating unit 3 and with an increasing image-end numerical aperture of the projection objective 5.

According to another feature of the invention, the illumination unit can be a light source for emitting ultraviolet laser light.

In FIG. 2, a projection objective for microlithography is shown. This objective includes six lens groups.

The first lens group includes three positive lenses L101 to L103, which are all biconvex. The last lens L103 is provided with an asphere on the image-end surface. A targeted correction of the coma in the region of the image field zone is possible via the aspheric surface provided forward of the first waist or narrowing. The aspheric lens surface has only a slight influence on the inclined spherical aberration in the tangential section and in the sagittal section. In contrast, the inclined sagittal aberration (especially in the region between the image field zone and the image field edge) can be corrected with the aspherical lens surface after the narrowing or waist.

The provision of a second aspherical lens surface is a valuable measure in order to counter, with an increased aperture, a reduction of the image quality based on coma.

The second lens group includes four lenses L104 to L107. The image-end mounted lens surface of this last lens L107 of the second lens group includes an aspheric lens surface. By means of this aspheric lens surface, especially a correction of image aberrations in the region between the image field zone and the image field edge is possible. The aberrations of higher order, which become noticeable with the observation of sagittal sections, are corrected. This is an especially valuable contribution because these aberrations, which are apparent in the sagittal section, are especially difficult to correct.

The third lens group includes the lenses L108 to L111. This lens group has a positive refractive power. The last image-end disposed lens surface of the last lens of this group is aspheric. This asphere operates, on the one hand, advantageously on the coma and, on the other hand, this asphere operates in a correcting manner on the axial aberration and on the inclined spherical aberration. The correction of the aberration is especially possible because of the large beam diameter in the region of this aspheric surface.

The following lens group having the lenses L112 to L115 has a negative refractive power.

The lens group following the above has a positive refractive power and includes lenses L116 to L123. A diaphragm is mounted in this lens group and this diaphragm is provided after the lens L119 so that four lenses of positive refractive power are mounted forward of the diaphragm. The excellent correction of the aberrations of this objective is attributable primarily to the positive lenses forward of the diaphragm. These lenses have a large component focal length because of the large diameter thereof, whereby the field loading drops and an improved correction at a higher numerical aperture is possible. These positive lenses operate, inter alia, advantageously on the coma. Furthermore, this lens group is characterized by a reduced number of lenses.

The sixth and last lens group includes the lenses L124 to L127. The precise data of the lenses are presented in Table 1. The image field is 8×26 mm. It is noted that this objective has a very significantly high numerical aperture and yet has only 27 lenses. The required space for this objective is 1000 mm. The precise lens data are presented in Table 1.

TABLE 1 ½ Lens Refractive Index Lenses Radius Thickness Material Diameter at 248 nm 0 infinite 20.9706 L710 61.246 0.999982 L101 1160.20105 13.5756 SIO2 66.130 1.508373 −363.46168 0.7500 L710 66.788 0.999982 L102 256.92295 20.1184 SIO2 68.174 1.508373 −429.93637 0.7500 L710 67.973 0.999982 L103 353.94471 15.3795 SIO2 66.245 1.508373 −1064.34630 A 0.7500 L710 65.385 0.999982 L104 365.62225 10.0788 SIO2 62.164 1.508373 150.28204 24.6344 L710 57.665 0.999982 L105 −160.21163 7.0000 SIO2 57.121 1.508373 138.69010 21.4314 L710 57.066 0.999982 L106 −257.68200 7.0000 SIO2 57.709 1.508373 280.52202 27.7747 L710 62.688 0.999982 L107 −122.86419 7.000 SIO2 64.152 1.508373 −524.02005 A 21.2270 L710 75.975 0.999982 L108 −334.99360 27.7619 SIO2 88.903 1.508373 −142.00372 0.7500 L710 92.514 0.999982 L109 −1079.51219 40.8554 SIO2 109.187 1.508373 −172.00795 0.7500 L710 111.327 0.999982 L110 438.67858 43.4000 SIO2 122.583 1.508373 −378.94602 0.7500 L710 122.708 0.999982 L111 162.42382 51.1885 SIO2 113.015 1.508373 −5736.26278 A 0.7500 L710 110.873 0.999982 L112 165.15494 14.7530 SIO2 92.577 1.508373 110.95539 37.6018 L710 79.631 0.999982 L113 −2352.60464 7.0000 SIO2 78.360 1.508373 158.84317 34.9167 L710 71.086 0.999982 L114 −168.34448 7.0000 SIO2 70.590 1.508373 245.44885 39.3735 L710 71.824 0.999982 L115 −113.75821 7.0000 SIO2 72.408 1.508373 666.85880 23.5469 L710 88.173 0.999982 L116 −278.47485 16.7462 SIO2 90.415 1.508373 −195.62311 0.7500 L710 95.097 0.999982 L117 1596621.30490 37.6629 SIO2 113.071 1.508373 −223.02293 0.7500 L710 115.353 0.999982 L118 2651.21287 31.3744 SIO2 127.060 1.508373 −371.06734 0.7500 L710 128.117 0.999982 L119 1313.12466 25.1961 SIO2 131.302 1.508373 −666.16100 0.0 131.498 1.000000 infinite 9.5632 L710 130.856 0.999982 Diaphragm 0.0 130.856 L120 812.62806 22.4028 SIO2 132.498 1.508373 −1458.91764 10.9629 L710 132.481 0.999982 L121 344.45037 42.1137 SIO2 130.307 1.508373 −765.47811 29.1268 L710 129.380 0.999982 L122 −250.24553 7.000 SIO2 127.451 1.508373 −632.30447 15.5964 L710 127.304 0.999982 L123 −398.61314 20.5840 SIO2 126.393 1.508373 −242.62300 1.2010 L710 126.606 0.999982 L124 143.95358 37.1050 SIO2 103.455 1.508373 419.96225 0.8946 L710 100.698 0.999982 L125 120.37736 30.9217 SIO2 85.039 1.508373 263.87928 14.8885 L710 79.055 0.999982 L126 1886.79345 7.6305 SIO2 74.319 1.508373 277.58693 3.7474 L710 65.935 0.999982 L127 144.27214 50.1938 SIO2 58.929 1.508373 423.41846 15.0000 L710 32.250 0.999982 0′ infinite 0.0001 L710 13.602 * 0.999982 L710 is air at 950 mbar.

ASPHERE L103: EX = 0 C1 = −0.10457918*10⁻⁶ C2 = 0.37706931*10⁻¹¹ C3 = 0.61848526*10⁻¹⁶ C4 = −0.13820933*10⁻¹⁹ C5 = 0.36532387*10⁻²⁴ C6 = −0.11262277*10⁻²⁸ ASPHERE L107: EX = 0.4532178*10² C1 = 0.19386780*10⁻⁷ C2 = −0.22407622*10⁻¹¹ C3 = −0.42016344*10⁻¹⁵ C4 = 0.45154959*10⁻¹⁹ C5 = −0.19814724*10⁻²³ C6 = −0.43279363*10⁻²⁸ ASPHERE L111: EX = 0 C1 = 0.57428624*10⁻⁸ C2 = 0.22697489*10⁻¹² C3 = −0.71160755*10⁻¹⁸ C4 = −0.72410634*10⁻²¹ C5 = 0.32264998*10⁻²⁵ C6 = −0.55715555*10⁻³⁰

The aspheric surfaces are described by the equation:

${P(h)} = {{\frac{\delta \cdot h \cdot h}{1 + \sqrt{1 - {\left( {1 - {EX}} \right) \cdot \delta \cdot \delta \cdot h \cdot h}}} + {C_{1}h^{4}} + \ldots + {C_{n}h^{{2n} + 2}\mspace{65mu}\delta}} = {1/R}}$ wherein: P is the arrow height as a function of the radius h (height to the optical axis 7) with the aspherical constants C₁ to C_(n) presented in Table 1; R is the apex radius and is given in the table.

In FIG. 3, a projection objective is shown for the wavelength 193 nm and has a numerical aperture of 0.8. A field of 8×26 can be exposed by means of this objective. The required structural space of this objective is 1000 mm.

The first lens group includes only two positive lenses and both are biconvex. The first lens L201 of this lens group G1 is provided with an aspheric lens surface at the object end.

The second lens group G2 includes the lenses L203 to L205. The lens L203 is provided with an aspheric lens surface at the object end. Because of the two aspheric lens surfaces of the lenses L201 and L203, which are provided in the first and second lens groups (G1, G2), respectively, and are arranged so as to be close to the field, an excellent beam separation in the input region of the objective is obtained. The arrangement of the aspheric lens surfaces on the side, which faces to the object, affords the advantage that the lenses, which have an aspheric lens surface, lie with the spherical lens surface against a lens frame. In this way, an excellent contact engagement on the lens frame with the spherical lens surface can be more easily ensured.

The third lens group G3 includes the lenses L206 to L210. This lens group has a positive refractive power. The two lenses L208 and L209 have two surfaces greatly curved toward each other. The last lens L210 of this lens group includes, at the image end, an aspheric lens surface. An excellent coma correction can be carried out by means of this aspheric lens surface. Furthermore, a correction of the axial and inclined spherical aberrations is especially possible in this region because of the large beam diameters.

The fourth lens group includes lenses L211 to L214. This lens group overall has a negative refractive power. In the next and fifth lens group G5, which includes the lenses L215 to L220, the diaphragm is mounted after the lens L217. This lens group includes three positive lenses and the last lens forward of the diaphragm is configured to be especially thick. The last lens group G6 includes the lenses L221 to L225 and the lens L224 is configured to be especially thick. An intense spherical overcorrection is obtained with this lens.

The precise lens data is presented in Table 2.

TABLE 2 ½ Lens Refractive Index Lenses Radius Thickness Material Diameter at 193 nm 0 infinite 32.7500 L710 61.249 0.999982 L201 469.70813 A 14.5480 SIO2 62.591 1.560289 −20081.10295 5.1612 HE 63.071 0.999712 L202 354.86345 18.8041 SIO2 63.983 1.560289 −334.15750 9.4004 HE 63.889 0.999712 L203 381.44025 A 28.0599 SIO2 61.107 1.560289 140.16853 27.1615 HE 55.898 0.999712 L204 −149.89590 23.2652 SIO2 55.910 1.560289 229.41466 33.1065 HE 62.024 0.999712 L205 −105.40274 7.0000 SIO2 63.462 1.560289 −336.55620 16.9549 HE 74.238 0.999712 L206 −165.03805 10.7419 SIO2 78.416 1.560289 −147.21753 0.7575 HE 82.164 0.999712 L207 −314.39712 27.7710 SIO2 90.707 1.560289 −145.41305 0.7500 HE 94.176 0.999712 L208 −50326.68803 38.7705 SIO2 107.592 1.560289 −211.33124 0.7500 HE 109.537 0.999712 L209 184.32395 41.8364 SIO2 112.438 1.560289 1282.45923 0.7500 HE 110.470 0.999712 L210 153.97703 35.8150 SIO2 99.821 1.560289 538.04124 A 8.4636 HE 95.507 0.999712 L211 180.72102 7.8641 SIO2 82.558 1.560289 116.94830 38.5761 HE 73.768 0.999712 L212 −292.06054 7.0000 SIO2 71.989 1.560289 121.89815 26.8278 HE 65.096 0.999712 L213 −416.86096 7.0000 SIO2 65.191 1.560289 320.06306 34.0097 HE 66.681 0.999712 L214 −106.74033 7.1599 SIO2 67.439 1.560289 842.66128 12.4130 HE 82.767 0.999712 L215 −531.44217 35.2270 SIO2 84.311 1.560289 −173.85357 0.7500 HE 93.111 0.999712 L216 5293.05144 34.6817 SIO2 109.462 1.560289 −359.30358 5.8421 HE 114.271 0.999712 L217 1423.10335 73.8658 SIO2 123.709 1.560289 −302.64507 11.7059 HE 130.054 0.999712 infinite −4.1059 HE 129.751 0.999712 infinite 0.0000 129.751 L218 644.68375 29.3314 SIO2 130.947 1.560289 −1224.04524 0.7500 HE 130.998 0.999712 L219 324.02485 28.7950 SIO2 129.211 1.560289 1275.35626 44.6599 HE 127.668 0.999712 L220 −246.29714 25.7695 SIO2 126.964 1.560289 −260.21284 0.7500 HE 129.065 0.999712 L221 265.62632 25.9894 SIO2 115.965 1.560289 689.74229 1.8638 HE 113.297 0.999712 L222 148.08236 25.7315 SIO2 100.768 1.560289 256.32650 14.8743 HE 97.685 0.999712 L223 130.15491 28.8792 SIO2 81.739 1.560289 554.81058 6.6463 HE 77.855 0.999712 L224 infinite 67.6214 CAF2HL 76.291 1.501436 infinite 0.9000 HE 33.437 0.999712 L225 infinite 4.0000 SIO2 32.220 1.560289 0′ infinite L710 29.816 0.999982 L710 is air at 950 mbar.

ASPHERE L201: EX = 0 C1 = 0.98184588*10⁻⁷ C2 = −0.34154428*10⁻¹¹ C3 = 0.15764865*10⁻¹⁵ C4 = 0.22232520*10⁻¹⁹ C5 = −0.79813714*10⁻²³ C6 = 0.71685766*10⁻²⁷ ASPHERE L203: EX = 0 C1 = 0.26561042*10⁻⁷ C2 = 0.78262804*10⁻¹² C3 = −0.24383904*10⁻¹⁵ C4 = −0.24860738*10⁻¹⁹ C5 = 0.820928858*10⁻²³ C6 = −0.85904366*10⁻²⁷ ASPHERE L210: EX = 0 C1 = 0.20181058*10⁻⁷ C2 = −0.73832637*10⁻¹² C3 = 0.32441071*10⁻¹⁷ C4 = −0.10806428*10⁻²¹ C5 = −0.48624119*10⁻²⁵ C6 = 0.10718490*10⁻²

In FIG. 4, a further lens arrangement 19 is shown which is designed for the wavelength 248 nm. This lens arrangement includes 25 lenses which can be subdivided into six lens groups. The structural length of this lens arrangement from object plane 0 to image plane 0′ is 1000 mm. The numerical aperture of this lens arrangement is 0.8 of the image end.

The first lens group G1 includes two positive, biconvex lenses L301 and L302. The lens L301 is provided with an aspheric lens surface at the object end.

The second lens group G2 has negative refractive power and includes the lenses L303 to L305. The lens L303 is provided with an aspherical lens surface at the object side. An excellent correction of field aberrations is possible with these two aspheric lens surfaces of the lenses L301 and L303. Furthermore, a clear beam separation is achieved because of these aspheres mounted close to the field.

The third lens group G3 includes the lenses L306 to L310 and has a positive refractive power. The lens L310 is provided with an aspheric lens surface at the image end. By means of this aspheric lens surface, an especially good correction of the coma and the axial and inclined spherical aberrations is possible. An arbitrated correction between axial and inclined spherical aberrations is especially possible because of the large beam diameters which are, however, significantly less than the clear lens diameters.

The fourth lens group G4 comprises the lenses L311 to L314 and has a negative refractive power.

The fifth lens group G5 includes the lenses L315 to L320 and has an overall positive refractive power. A diaphragm AP is mounted after the lens L317. By providing the clear air space between lens L317 and lens L318, it is possible to arrange a slide diaphragm between these two lenses.

The sixth lens group G6 includes the lenses L321 to L325. This lens group likewise has a positive refractive power. The meniscus lenses L321 to L323 are curved on both sides toward the object. This lens group includes only concave lenses which effect a field-independent, intense spherical overcorrection. For objectives having a high aperture, a correction of the spherical aberration also of higher order is possible by means of such conversion lenses.

This objective is especially well corrected especially because of the use of the aspheric lens surfaces as well as because of the specific arrangement of the number of positive lenses of the first lens group and because of the higher number of positive lenses forward of the diaphragm. The deviation from the wavefront of an ideal spherical wave is a maximum of 5.0 mλ for a wavelength of 248 nm.

Preferably, the aspheric lens surfaces are arranged on the forward lens surface whereby the corresponding lens lies with its spherical lens surface on the frame surface. In this way, these aspherical lenses can be framed with standard frames. The precise lens data are presented in Table 3.

TABLE 3 M1652a REFRACTIVE INDEX ½ FREE SURFACE RADII THICKNESSES GLASSES 248.338 nm DIAMETER 0 infinite 32.750000000 L710 0.99998200 54.410 1 480.223886444 AS 16.335451604 SIO2 1.50839641 62.519 2 −1314.056977504 2.406701682 L710 0.99998200 63.128 3 329.047567482 20.084334424 SIO2 1.50839641 63.870 4 −305.091682732 4.977873027 L710 0.99998200 63.737 5 383.800850809 AS 34.498893572 SIO2 1.50839641 61.345 6 132.468446407 27.572735356 L710 0.99998200 54.949 7 −146.238861297 7.000000000 SIO2 1.50839641 54.908 8 202.067070373 26.902804948 L710 0.99998200 58.294 9 −124.60415239 7.000000000 SIO2 1.50839641 59.529 10 −9484.579900199 32.328722869 L710 0.99998200 69.147 11 −199.920035154 13.239699068 SIO2 1.50839641 80.852 12 −156.061108055 0.750000376 L710 0.99998200 84.387 13 −647.599685325 32.765465982 SIO2 1.50839641 96.077 14 −169.327287667 0.750000000 L710 0.99998200 99.492 15 54987.154632328 43.791248851 SIO2 1.50839641 110.237 16 −198.179168899 0.750000000 L710 0.99998200 112.094 17 179.965671297 37.961498762 SIO2 1.50839641 110.618 18 730.008903751 0.750000000 L710 0.99998200 108.526 19 155.802150060 40.190627192 SIO2 1.50839641 99.471 20 525.570694901 AS 3.398727679 L710 0.99998200 93.056 21 210.625893853 10.671567855 SIO2 1.50839641 85.361 22 118.365024068 39.388505884 L710 0.99998200 74.596 23 −290.993996128 7.000000000 SIO2 1.50839641 72.941 24 153.643732808 24.440280468 L710 0.99998200 67.256 25 −364.763623225 7.000000000 SIO2 1.50839641 67.177 26 201.419421908 40.566258495 L710 0.99998200 68.276 27 −109.336657265 7.000000000 SIO2 1.50839641 69.319 28 1061.293067334 13.765515688 L710 0.99998200 84.656 29 −569.739152405 43.187833722 SIO2 1.50839641 87.749 30 −187.461049756 0.750000000 L710 0.99998200 99.718 31 1880.153525684 40.009394091 SIO2 1.50839641 117.515 32 −286.975850149 0.750000000 L710 0.99998200 120.535 33 1960.535354230 35.788625356 SIO2 1.50839641 127.909 34 −378.322213808 11.705900000 L710 0.99998200 129.065 35 infinite −4.105900000 L710 0.99998200 129.546 36 665.988216308 27.299895961 SIO2 1.50839641 130.708 37 −1514.956732781 0.750000000 L710 0.99998200 130.863 38 392.166724592 35.529695156 SIO2 1.50839641 130.369 39 −2215.367253951 37.377386813 L710 0.99998200 129.155 40 −235.632993037 38.989537996 SIO2 1.50839641 128.458 41 −252.020337993 0.835229633 L710 0.99998200 131.819 42 269.631401556 32.688617719 SIO2 1.50839641 118.998 43 1450.501345093 0.750000001 L710 0.99998200 116.187 44 138.077824305 29.652384517 SIO2 1.50839641 100.161 45 255.416969175 2.589243681 L710 0.99998200 96.793 46 139.090220366 30.752909421 SIO2 1.50839641 86.930 47 560.532964454 8.142484947 L710 0.99998200 82.293 48 infinite 73.619847203 SIO2 1.50839641 79.524 49 infinite 0.900000000 L710 0.99998200 33.378 50 infinite 4.000000000 SIO2 1.50839641 32.173 51 infinite 12.000000000 L710 0.99998200 29.666 52 infinite 13.603 L710 is air at 950 mbar.

ASPHERIC CONSTANTS SURFACE NO. 1 EX  0.0000 C1  9.53339646e−008 C2 −3.34404782e−012 C3  1.96004118e−016 C4  8.21742864e−021 C5 −5.28631864e−024 C6  4.96925973e−028 C7  0.00000000e+000 C8  0.00000000e+000 C9  0.00000000e+000 SURFACE NO. 5 EX  0.0000 C1  2.89631842e−008 C2  7.74237590e−013 C3 −2.72916513e−016 C4 −8.20523716e−021 C5  4.42916563e−024 C6 −5.10235191e−028 C7  0.00000000e+000 C8  0.00000000e+000 C9  0.00000000e+000 SURFACE NO. 20 Ex  0.0000 C1  1.99502967e−008 C2 −7.64732709e−013 C3  3.50640997e−018 C4 −2.76255251e−022 C5 −3.64439666e−026 C6  5.10177997e−031 C7  0.00000000e+000

It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. 

1. A projection objective defining an image plane and comprising, in sequence: an object plane; a first lens group of positive refractive power adjacent said object plane; a second lens group of negative refractive power; a third lens group of positive refractive power including meniscus lenses; at least one additional lens group having positive refracting power and having a diaphragm mounted therein; said second lens group including a plurality of negative lenses; said projection objective defining an image plane; a distance between each negative lens of said second lens group; said distance between each negative lens of said second lens group and said image plane being greater than 54 percent of the object plane to image plane distance; and, a lens of one of said lens groups being an aspheric lens.
 2. A projection objective defining an image plane and comprising, in sequence: an object plane; a first lens group of positive refractive power adjacent said object plane; a second lens group of negative refractive power; a third lens group of positive refractive power consisting of meniscus lenses; at least one additional lens group having positive refracting power and having a diaphragm mounted therein; and, said projection objective having a numerical aperture of at least 0.8.
 3. A projection objective defining an optical axis and an image plane and comprising: an object plane; a plurality of lenses arranged along said optical axis; a diaphragm interposed between two of said lenses; a first one of said lenses being an aspheric lens; a second one of said lenses being arranged between said diaphragm and the image plane; and, said second lens having a thickness of about at least 6 cm.
 4. The projection objective of claim 3, wherein said thickness of said second lens is measured at said optical axis.
 5. The projection objective of claim 4, wherein said second lens has a varying thickness.
 6. The projection objective of claim 4, wherein said second lens is a plane-parallel plate.
 7. A projection objective defining an optical axis and an image plane and comprising: an object plane; a plurality of lenses arranged along said optical axis; a diaphragm interposed between two of said lenses; a first one of said lenses being an aspheric lens; a second one of said lenses being arranged between said diaphragm and the image plane; said second lens having a thickness of about at least 6 cm; and, said projection objective having a numerical aperture of at least 0.8.
 8. A projection objective defining an optical axis and an image plane and comprising: an object plane; a plurality of lenses arranged along said optical axis; a diaphragm interposed between two of said lenses; a first one of said lenses being an aspheric lens; a second one of said lenses being arranged between said diaphragm and the image plane; said second lens having a thickness of about at least 6 cm; and, a plane-parallel plate.
 9. The projection objective of claim 8, wherein said plane-parallel plate follows said second lens. 